McCain, a former chairman of the committee on Indian Affairs, said Harper has refused to answer his questions regarding his negotiation of Cobell v. Salazar — a $3.4 billion class-action lawsuit settlement over misspent Native American land royalties.

“I never got an answer,” McCain told The Hill. “I never got any answer to the questions that I asked. It’s as simple as that.”

The State Department did respond to a list of questions for the record that McCain submitted shortly after the hearing, according to State Department spokesman Alec Gerlach.

A McCain said Harper’s answers weren't satisfactory.

At the hearing, McCain said he could not support the nomination, citing a letter released by the Cobell team — on which Harper served as co-counsel. McCain called it an “abuse” of human rights.

The 2012 letter revealed the contact information of four Native Americans who were in the process of appealing the settlement Harper helped negotiate. The letter was released to 500,000 class members and blamed the appellants for holding up their funds.

Harper responded that he had nothing to do with the missive. He blamed his co-counsel on the case, Dennis Gingold, for writing and posting the letter online.

“Why didn’t he say something against it, when he knew something, when that letter was going out?” McCain told The Hill. “And why didn’t he condemn it, even afterwards? He didn’t.”

Harper has offered to meet with McCain, but the Arizona senator has not responded, according to the State Department.

Sen. John Barrasso (R-Wyo.), a member of the Foreign Relations panel, also vowed to investigate Harper’s past dealings with tribes. He still has concerns, but his press office did not comment further.

Sen. Barbara Boxer (D-Calif.), who chaired the hearing this fall, said she was “blindsided” by McCain’s accusations, and said at the time: “I agree with [McCain] that this is a problem.” She also urged Harper to provide more information to the committee.

Boxer now approves of the nomination; Gingold assured her staff that Harper was not involved with the controversial letter.

“It’s a history-making nomination and I hope the Senate moves soon on his nomination,” Boxer said in a statement released by her press office.

There are pending legal cases surrounding the Cobell settlement. The State Department declined to comment on the legal disputes.